The hill-holding problem has been long recognized and has been resolved in various ways in the prior art. The problem is incurred, typically, by braking a vehicle for a traffic signal on an upwardly inclined roadway, then removing the foot from the brakes to move the vehicle forward. Thus, the vehicle can move backward before the engine is engaged to transmit enough power to overcome the tendency to move backward. Sometimes there is a problem with heavy loads and on steep inclines that more than normal manual braking force is necessary, so that backward vehicle motion may occur unexpectedly if the driver does not consciously keep the brake pedal jammed down. There is at least in the interim time when the foot is moved from the brake to the accelerator pedal when the vehicle tends to move backward down the incline, an accompanying danger to a following vehicle or pedestrian. This tendency is even more pronounced in vehicles operated by a clutch, which disconnects the engine power from the drive drain so that the tendency to roll backward is unimpeded by engine braking.
A prior art class of hill-holding braking systems using the depression of the clutch pedal to operate the vehicle brakes, is typified by the following U.S. Patents: A. G. Taig, et al., U.S. Pat. No. 4,582,184, Apr. 15, 1986 for Brake Control Device; A. Mizuno, U.S. Pat. No. 4,093,050, Jun. 6, 1978 for Clutch and Accelerator Controlled Brake Lock for Vehicles; J. Y. Ha, U.S. Pat. No. 4,515,259, May 7, 1985 for Clutch-Operated Hill Holder Brake System; Y. K. Kim, U.S. Pat. No. 687,080, Aug. 18, 1987 for Clutch Brake Method; K. Kojima, et al., U.S. Pat. No. 4,802,563, Feb. 7, 1989 for Braking Force Holding Device for an Air Brake System; and S. L. Radcliffe, et al., U.S. Pat. No. 3,923,127, Dec. 2, 1975 for Vehicle Braking System. However, these systems are not operable with vehicles having automatic transmissions. Furthermore even if the brakes are applied by the clutch, particularly under loaded conditions or on steep hills, a vehicle will move backward in the interim when the foot is moved from the clutch to the accelerator to engage gears and apply enough engine power to move forward.
Another class of brake control devices rely upon the sensing of an inclined vehicle position to apply the brakes. Typical U.S. Patents are S. Shoji, et al., U.S. Pat. No. 4,247,154, Jan. 27, 1981 for Brake Control Valve; W. K. Messersmith, et al., U.S. Pat. No. 4,660,691, Apr. 28, 1987 for Vehicular Hill Holder System Having a Control Circuit Responsive to Vehicular Attitude, Clutch Position, and Gear Position; and A. G. Taig, U.S. Pat. No. 4,538,710, Sept. 3, 1985 for Mechanical Brake Control Device. However, it is not the inclination of the vehicle that causes potential damage requiring correction, but the actual backward movement of the vehicle. For example, if a rear wheel enters a rut or pothole, an inclination might be detected and thus the brakes may become locked in place under undesirable circumstances.
Also, there are some braking control systems that tend to alter the drivers normal braking sequence or habits when stopping and restarting on an upwardly inclined roadway. This is not safe, since it requires judgment when the roadway is inclined upwardly, a perspective that is not certain from visual inspection. Also, it is preferable to drive normally without having to learn to operate a special braking procedure, or to rely upon a hill-holding brake feature so that precautionary driving measures are not habitually used. Thus, a driver is expected under normal circumstances to be alert to the danger of backward motion on inclines and to use the brakes, transmission and accelerator in such a manner as to prevent backward roll under usually encountered conditions, with no fail safe provisions in the event of an error of judgement.
Other problems with such prior art devices include the failure to provide a system operable substantially universally over a wide range of different vehicles with braking systems that may be operated mechanically, hydraulically or with air. In this respect mechanically actuated and reacting systems are difficult to install and may require alterations of vehicle body structure or mechanisms. Nor are the prior art systems in general adapted to simply retrofit a hill-holding braking system by installation upon existing vehicles after manufacture without significant alteration of the vehicle.
It is accordingly an object of the invention to overcome the foregoing prior art problems and to provide an improved and simplified safety override brake control system operable for hill holding without disturbing operator control except under those conditions when actual backward motion is sensed on inclined roadways without engagement of the vehicle reverse gear.
Other objects, features and advantages of the invention will be found throughout the following description, drawings and claims.